HUT76649A - Cross-layered, multi-layered film structures for making bank notes or the likes - Google Patents

Abstract

A laminated multi-layer film substrate comprises layers (a) and (b) each comprising at least 50 wt. % HDPE with density of at least 0.94 and oriented in 1 direction at least 3 times more than in the direction normal to the first and laminated so that the directions of major orientation are aligned. - Pref., both (a) and (b) comprise propylene polymer skin(s), pref. on both the inner and outer sides, and pref. comprising 10-20 wt. % LDPE. (b) is thermally laminated to (a). A laminating adhesive (c), pref. LDPE and/or LLDPE is used between (a) and (b), pref. with a primer between (a)/(b) and (c), the latter esp. being of ABA construction with a core layer (B) of LLDPE and layers (A) of LDPE. The substrate pref. further comprises a security device (d) between (a) and (b), esp. between the primer coatings on the inner sides of (a) and (b).

Description

The present invention relates to a multilayer film for use in the manufacture of paper products such as banknotes and securities, such as travel and bank checks, and to a process for the production thereof. More particularly, the present invention relates to a laminated multilayer film structure having the characteristics of high-quality papers commonly used in the production of banknotes and securities.

For the production of banknotes and securities, wood-free paper has been used for over 300 years. As • ·

well known, wood-free paper has many of the features that are highly desirable for such applications, such as dead foldability, tear resistance, printability, and gravity printing.

These highly desirable properties are characterized by the ability of a material to be folded or folded and hold the fold without splitting; tensile strength is the ability of a material to withstand both started and non-started tears and punctures; printability means the ability of a material to absorb and bind inks during a printing process; gravity is the ability of a material to deform under the presses of an embossing process to give an embossed image on the produced banknote or security, the ink of the intaglio remaining on the embossed deformed portion, thereby giving the banknote or security a high degree of tact or grip. It will be appreciated that these features together give the usual grip and functionality of banknotes and the like.

With the advent of color copiers and computer scanners, the counterfeiting of banknotes has increased significantly. While the main producers of banknote paper are developing effective programs to make their materials more secure by using watermarks, metal fibers and optical variable devices (OVDs) such as color photography, holograms and diffraction grids, these efforts do not offer much hope for counterfeiters.

Plastics are more secure if a transparent window is built into the banknote. This window ensures that a scanner or color copier cannot copy the banknote. In addition, other security features can be added to or affixed to the banknote, such as the back printing of the banknote, security features, and pressure protection.

• ·

The present invention provides a laminated multilayer film material for use in the production of banknotes and securities. The film material comprises a first layer comprising at least 50% by weight of high density polyethylene having a density of at least 0.95, said first layer being stretched in a first direction at least three times greater than the degree of stretching. present in a direction substantially perpendicular to the first direction; and a second layer comprising at least 50% by weight of high density polyethylene having a density of at least 0.95, the second layer being stretched in a first direction at least at least three times the amount of stretching in the first direction. present in a substantially perpendicular direction; in addition, the second layer is laminated to the film material such that the first stretching direction of the second layer is substantially perpendicular to the first stretching direction of the first layer.

The foils produced in this manner exhibit good foldability and other properties which make them suitable for the production of banknotes and other securities.

In the production of multilayer film materials for use in the production of banknotes and other securities according to the invention, at least two layers of material must contain a high proportion of high density polyethylene (HDPE) having a density of at least 0.95. These film layers may be made exclusively of an HDPE resin, a mixture of HDPE resins, or an HDPE resin containing a lower proportion of another polymeric material such as low-density polyethylene, linear low-density polyethylene, polypropylene, ethylene-vinyl alcohol (EVOH) copolymer, ethylene-propylene (EP) copolymer or ethylene-propylene-butene-1 (EPB) copolymer, but a single HDPE resin or a mixture of HDPE resins is particularly advantageous for carrying out the process of the invention. For processing, additives such as microcrystalline wax or the like can be used with the preferred HDPE resins to make the extruder more tiltable. can be reduced, reducing the torsion torque of the extruder. We have found that films made with a mixture of HDPE resins or microcrystalline wax have a reduced tendency for the film to break, which is manifested by its tendency to rupture in the transverse direction.

When mixtures of HDPE polymers are used, these mixtures may contain two or more polymers, each preferably having a density of 0.95 or more. Mixtures of HDPE polymers preferably contain a greater proportion of HDPE resin having a melt index of 0.6 to 1.2 and one or more polymers having a different melt index.

Triple blends are also preferred. Suitable triple blends are generally 50-98% by weight, preferably 84-96% by weight, of HDPE resin having a density of 0.96 or higher and a melt index greater than 0.5-2.0, 1-25% by weight, preferably 3-8% by weight of HDPE resin having a density of 0.96 or more and a melt index of 0.1-0.5, and 1-25% by weight, preferably 3-8% by weight of HDPE resin having a density of 0 , 96 or greater, and a melt index greater than 2-8. The second and third HDPE polymers, which are minor components, are preferably present in about the same amount.

As will be described in more detail below, it has been found that the direction-dependent tensile strength in a multilayer film material is significantly improved by laminating at least two layers of the multilayer film material so that the main (basic) stretching directions of these layers are aligned to one another. be substantially perpendicular. This improvement in tensile strength, combined with the excellent folding, gravure printing and printability of HDPE resins, provides a multilayer film structure that has long been desired in the production of banknotes and securities.

As particularly preferred, the film material of the invention comprises a first layer of at least

% by weight of high density polyethylene having a density of at least 0.95, said first layer being stretched in a first direction at least three times greater than the degree of elongation substantially perpendicular to the first direction; and a second layer, which also contains at least 50% by weight of high density polyethylene having a density of at least 0.95, said second layer being stretched in a first direction at least three times greater than the degree of stretching. is substantially perpendicular to the first direction, and the second layer is laminated to the film material such that the first stretching direction of the second layer is substantially perpendicular to the first stretching direction of the first layer.

It will be appreciated that in order to achieve tensile strength improvement in the multilayer film of the type described, it is not necessary that the first and second HDPE film layers be stretched only unilaterally, since it has been found that unbalanced biaxially stretched HDPE they are perpendicular to one another - they can be made in essentially the same way. The process for making unbalanced biaxial stretch HDPE films is described in U.S. Patent 4,870,122.

The degree of elongation of the HDPE film layers is an important feature of the present invention since the proper degree of stretching provides the required physical properties. Although a higher density HDPE resin having a density of 0.957 or higher can be made directly by film extrusion (molding), there is a problem of creasing, unevenness and flatness. Therefore, thin HDPE films of 0.02-0.04 mm (0.8-1.5 ml) are obtained which have the best balance of properties using unbalanced biaxially stretched films of 0.3-0.5 mm (12 mm). -20 mii) from films of casting thickness and stretched to the desired thickness.

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The films are prepared and stretched in a conventional manner. The film is heated to its stretching temperature and first subjected to a longitudinal (machine) stretching between two sets of tension rollers, wherein the second roll rotates at a higher speed than the first to an extent that corresponds to the desired tensile ratio. The film is then stretched transversely by heating and subjected to transverse stretching in a tensioning frame. Longitudinal stretching is generally performed at 60-120 ° C and transverse stretching is performed at 110-145 ° C.

While the degree of stretching in the first direction of the film is at least three times greater than the degree of stretching in a direction substantially perpendicular to the first direction, it is even more preferred that each HDPE film layer is 1.1 to 2.0 times it is stretched longitudinally and 6-12 times transversely. It has been found that HDPE film layers can be produced in high quality with a casting rate of up to 33.5 meters / min (110 fpm), which corresponds to a transmission rate of 46.9 meters / min (140 fpm) at 1.25 spray longitudinal stretch.

When applied, this degree of unbalanced elongation produces an interesting effect on the HDPE components of the structure. The result is a visibly wavy and ribbed appearance, where the waviness is parallel to the direction of transverse stretching. Under low magnification, each square centimeter of the HDPE film shows 5-30 discontinuous (intermittent) waviness and grooves, which are generally parallel to the direction of stretching. This effect gives the film a slightly translucent appearance, which makes distant objects slightly blurred when viewed through the film. This phenomenon indicates that the layers are stretched in an unbalanced manner. The high density polyethylenes useful in carrying out the process of the present invention are those described in U.S. Patent 4,870,122.

To achieve the desired surface characteristics of the paper products of the present invention, one or more surface layers may be applied in any known manner to the multilayer HDPE substrate, for example by coating or coextrusion before stretching, or by coating HDPE after one or both stretching operations. The surface layer may be any conventional material used for this purpose in connection with polyolefin films, in particular polyethylene films, for example, a polymeric resin may be mixed with fillers, fibers, pigments or the like, to produce a ready-to-print surface. Additionally, unfilled (gap) films such as those described in U.S. Patent Nos. 4,377,616, 4,632,869, and 4,758,462 and other U.S. Patent Nos. 4,706,462 and 4,778,462, may be applied to multilayer HDPE materials to provide the properties of such structures.

It should also be considered whether the material can be embossed, dyed, printed, textured or otherwise treated before or after layering; this may be done on the inner or outer surfaces of the laminate layers so that, for example, the nature, meaning or value of the banknote can be visually and / or tactfully identified.

Layering techniques that can be used to make the film structures of the present invention are known in the art and include the following operations: bonding or bonding with an adhesive, preferably a transparent material: solvent bonding, wherein spraying solvent is applied to the surfaces to be bonded; heat bonding, wherein the thermoplastic sheets are subjected to hot rolling or pressing operations; molding by layering, whereby one layer is poured onto another and the second layer forms the base material; or extrusion or tensile layering as is known in the art for calendering operations. If optically variable devices (OVDs) are used, they can be enclosed in pouches attached to the base material. On the other hand, optically variable devices themselves can be incorporated into one (or two) layers of the laminate or between the layers, it is not necessary to incorporate a physically separate device with a clearly defined pouch formed between the layers.

The term optically variable as used herein refers to any device (solution) that can be readily fabricated by altering its appearance (appearance) in a reversible, predetermined and reproducible manner. The appearance of these devices may vary, for example, by applying body heat or hand pressure, by changing the viewing angle (viewing angle), and by the lighting conditions under which they are viewed. Devices for use in the present invention include diffraction gratings, liquid crystals, moarem samples, and the like, which are made with crossed gratings, optionally with refracted, refracted, lens-shaped and transparent gratings such as lenses, partially opaque and partially opaque at the Press; coatings which result in variable interference patterns or the like: double or polarizing layers or zone sheets.

Optically active devices of this kind are usually readily recognized by inexperienced persons, but are very difficult to reproduce by photographic or printing techniques. In addition, the production of any such device in a reproducible manner and incorporation of such device into a plastic laminate, as described in the present invention, is likely to outweigh the ingenuity of the vast majority of those intending to counterfeit. Of course, when it comes to a flexible paper-like product, such as a banknote, it is advantageous if the optically variable devices themselves are flat, flexible and thin; it is also advantageous if these devices are compatible with the plastics used in the laminate to facilitate bonding and reduce reactive changes over time.

According to the present invention, the preferred form of the optically variable device is a reflective diffraction grating, which is a metallized thermoplastic film embossed with a diffraction pattern.

image. In order to prevent unauthorized copying of the embossed image, the present invention preferably uses a layer of thermoplastic on both sides of the metallized film which has similar solubility characteristics to the metal layer so that separation by preferential etching is very difficult. Another preferred tool is a moiré pattern, which reproduces a pattern of fine lines or dots on both sides of the thin film. The distances between dots and lines can easily be made so fine that they can be reproduced technically, yet the moire pattern only stands out on a much larger scale (shown). Diffraction and moireme alone are often used advantageously in banknotes and are known in the form of computer-generated and photoreduction methods for their production.

For the production of low denomination banknotes, you can only provide adequate security against counterfeiting by providing the banknote with a transparent window. As indicated above, such a window ensures that a banknote cannot be copied by a scanner or color copier. In addition, other security measures can be applied to the banknote or banknote, such as protecting the reverse (reverse) pressure of the banknote, security devices and imprint.

The multilayer film of the present invention can also be used in places where properties such as high durability and high quality printability are required, such as labels.

The invention is illustrated by the following examples. All parts in the examples are by weight unless otherwise specified.

Example 1 (Comparative)

The example film is prepared for comparison with the film of the invention.

- 10 1.15 ml final thickness multilayer stretch film material is coextruded on both sides with copolymer polypropylene topcoats to form the first layer (a). The HDPE resin used is Oxychem M6211 from Occidental Chemical Corporation, Dallas, Texas, having a density of 0.96 and a melt index of 1.0. The copolymer polypropylene coatings contain 90% Chisso 7510, an ethylene-propylene butene-1 terpolymer (triple copolymer) from Chisso Corporation of Japan, and 10% Mobil LKA-753, a low-density polyethylene from Mobil. Chemical Co., Norwalk, Connecticut. HDPE comprises 90% of the film layer (a) thus obtained and 10% (5% on each side) of the coatings. A second film layer (b) is formed which is identical to the film layer (a). The first films (a) and second (b) are stretched 1.4 times longitudinally at about H5 ° C; and 6-12 times, for example ten times transversely, at 115-140 ° C in a tensioning frame.

The copolymer topsheets on the inside of the elongated layers (a) and (b) are then coated with a polyethyleneimine (PEI) primer to form a total of 1.15 ml of OHD films.

The foil (a) may be provided with optically variable devices (OVDs) at predetermined distances from each other, thereby providing an optically variable device in the same location on each banknote ultimately produced from the foil.

Films (a) and (b) are laminated, including a laminating adhesive using LDPE (low density polyethylene) resin, Chevron 1017, manufactured by Chevron Chemical Co., Houston, Texas. The laminating adhesive resin undergoes stretching in the machine direction during the layering operation, thereby providing increased tear strength in the transverse direction. The layering is carried out by conventional methods to obtain a multilayer film material having a final thickness of about 3.0 ml; the laminating adhesive resin itself is about 0.7 mL thick. The material produced in this way has substantially pure physical properties in Table 1 ··· ·

- 11 to sum it up.

Example 2 (Comparative)

The procedure described in Example 1 was followed except that the laminating adhesive resin used was an LLDPE laminating grade adhesive resin, Dowlex 3010, available from Dow Chemical Co. of Midland, Michigan. The characteristics of the material produced are shown in Table 1. If higher molecular weight LLDPE is used as the adhesive resin in Example 2, the transverse tensile strength is increased.

Example 3

This example illustrates that the film materials of the present invention have improved abrasion resistance (wear resistance).

1.15 ml of final thickness multilayer stretched film material was coextruded with HDPE resin with copolymer polypropylene topcoats on both sides to form the first layer (a). The HDPE resin used is Oxychem M6211 from Occidental Chemical Corporation, Dallas, Texas, having a density of 0.96 and a melt index of 1.0. The copolymer polypropylene topcoats contain 90% Chisso 7510, an ethylene-propylene-butene-1 triple copolymer from Chisso Corporation of Japan, and 10% Mobil LKA-753, a low-density polyethylene manufactured by Mobil Chemical Co. , Manufactured by Norwalk, Connecticut. The HDPE resin constitutes 90% of the film layer (a) produced and 10% (5% on each side) of the topsheets. The film (a) is then stretched 1.4 times in the machine direction (MD) at about 115 ° C and 6-12 times, for example ten times at -140 ° C, in a stretching frame.

On the inner side of the elongated layer (a), the copolymer topcoats are then coated with a polyethyleneimine (PEI) primer to give a total OHD film of 1.15 ml.

The second film layer (b) is manufactured by Tenchi Kikai Kabushiki Kaisha, Sakai, Osaka Prefecture, Japan, made from HDPE resin having a melt index of 1-1.5 coextruded with a homopolymer polypropylene topcoat and stretched approximately 7-8 times in the machine direction; the film has a thickness of 0.95 ml, which is laminated to layer (a) using adhesive. The lamination is performed such that the transverse stretching of the second layer is substantially perpendicular to the transverse stretching of the first layer. The resulting laminate film has a total thickness of 2.5 ml and exhibits excellent tear strength in both machine direction (MD) and transverse direction (TD) at 22 ° C (72 ° F).

The physical properties of the films are summarized in Table 1.

Table 1

Example 1 Example 2 Example 3

Give me that thing MD 6 6 - (6.9 kPa x 10 ³ ) TD 16 20 - modulus MD 365 380 - Stiffness MD 17 20 - (G) TD 21 24 - Tensile strength MD 89 63 38 (G / mil) TD 4 5 34

Note: MD = Machine direction

ID = cross direction

Claims (9)

Claims Laminated multilayer film material comprising a first layer (a) and a second layer (b), which may be the same or different, each containing at least 50% by weight of high density polyethylene (HDPE) having a density of at least 0 95, each stretched in at least one first direction to an extent that is at least three times greater than the stretch in a second direction substantially perpendicular to the first direction; and the layer (b) is laminated to the layer (a) so that the first stretching direction of the layer (b) is substantially perpendicular to the first stretching direction of the layer (a). Film material according to Claim 1, characterized in that the degree of transverse stretching of the layers (a) and / or (b) is at least four times greater than the degree of machine extension (longitudinal). Film according to claim 1 or 2, characterized in that the layer (a) and / or (b) contains a higher proportion of a first HDPE resin having a density of 0.96 or higher and a melt index of 0.6. -1.2 and contains a second HDPE resin having a density of 0.96 or greater and a melt index other than the first HDPE resin. Film material according to any one of the preceding claims, characterized in that at least one of the layers (a) and (b) is unidirectional. Film material according to any one of the preceding claims, characterized in that the banknote comprises a transparent window. • · Film material according to any one of the preceding claims, characterized in that it comprises an optically variable device (VVD) between the layers (a) and (b). Film material according to any one of the preceding claims, characterized in that the optically variable device is at least one diffraction grating, a liquid crystal, a moiré pattern produced by a cross-grating, with or without superposition, refractive, lens-shaped and transparent gratings such as Fresnel lenses, a semi-transparent coating, thus providing variable interference patterns; double or polarizing layer or a zone plate. Film material according to claim 7, characterized in that the optically variable device is a reflective diffraction grating consisting of a metallized thermoplastic film embossed with a diffraction pattern. Film material according to any one of the preceding claims, in the form of a value indication, such as a banknote.